Woot! I've wanted to do this for awhile for Masako. Give a little voice to the face, no?
Anyway, I started watching the anime Sengoku Basara, and the voice of Maeda Matsu (which is the woman in the picture next to the Seiyuu) and I immediately kind of pictured that that's the most similar to what Masako sounds like in my head.
The name of the Seiyuu is Yuko Kaida, and here's a sample of what she sounds like:[link]
I might do one for my other female OC's as well :3